1. Field of the Invention
This invention relates to a wire facing unit for retaining walls and reinforced soil slopes that require placement of supporting struts at predetermined spacings along the width of the facing unit. The wire facing unit includes a built-in structural locator arrangement to provide a visual indication or reference for the installer to place the supporting struts at the correct locations.
2. Description of the Related Art
The formation of retaining walls such as Mechanically Stabilized Earth Walls (MSEW) and Reinforced Soil Slopes (RSS) and the use of reinforcing materials, such as geogrids for such structures is well known. The success of these structures relies not only on the reinforcing materials, but also on the manner in which the MSEW and RSS structures are installed. One of the main areas for poor construction technique is the wall or slope face. Under current design guidelines of the American Association of State Highway and Transportation Officials (“AASHTO”), MSEW and RSS structures may be constructed with a so-called wrap system, whereby a geogrid, typically a biaxial geogrid, is wrapped within a wire facing unit from the bottom surface above a floor section, then upward parallel to the face section, and then over the top fill surface to provide soil retention and, in the case of a RSS structures, possibly long-term face stability. This wrap technique is a very economical solution and has been utilized by many departments of transportation over the past two decades. However, face stability, compaction and geosynthetic placement is very difficult in wall and steep slope applications without the use of an effective face forming system employing wire facing units.
Known wire facing units typically are in the form of welded wire structures defining a rectangular-shaped face section and a rectangular-shaped floor section positioned angularly with respect to each other, preferably at a right angle. Support struts are selectively positioned along the width of the wire facing unit to provide strength and support. The width of such facing units are substantially greater than the height and depth of the facing unit. For example, the width may be ten feet and the height of the face section and depth of the floor section may be substantially smaller, e.g., 18 inches. Such wire facing units may be used with reinforcements, such as geogrid reinforcements, both uniaxial geogrids and biaxial geogrids. Fill material such as soil is located within the wall in the space defined by the face section and floor section. As such, the facing unit is subjected to high stresses and the welded wire facing units used in such temporary retaining walls typically require support struts positioned at predetermined, relatively precise locations to support the face section with respect to the floor section so that the loads that are applied to the walls do not cause sagging or bending of the facing unit. Current AASHTO specifications allows for a maximum outward bulge of the face section of 2 inches between strut connections. It has been found through experience in wall and slope installation that the installation of the support struts at 24 inches center to center maximum provides for the wall or slope face performing as intended and meeting the current AASHTO guidelines for face section alignment.
The installation of the support struts is performed on site. The installers first position a wire facing unit at the location where the wall is to be constructed and then install the wire struts at locations along the width of the wire facing unit. The installer may be told or instructed to install the wire struts at predetermined locations, for example every two feet, but errors in locating the wire struts can occur such that the wire struts may be located further apart from the required spacing, thus resulting in a weakened temporary retaining wall structure.
The known wire facing unit (sometimes referred to as a basket) while simple, does not provide the installer an easy way to make sure that the support struts are installed in the proper location. It is very common for the installer to space the struts beyond the predetermined maximum spacing requirement (i.e., beyond the prescribed two foot spacing) which can lead to excessive bulging beyond the current AASHTO allowance.